How to assign a specific weight to vertices? (instead of painting it)
Ah, I was fooling around and found an answer.


In the weight painting mode, use the Vertex selection masking for painting  V
Select wanted vertices for example with Circle select tool C
Set the wanted weight from Tool Shelf T
Weights -> Set Weight Shift+K




In addition, there's a useful addon for setting weight values:
http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Paint/Palettes